1. Field of the Invention
The invention relates generally to a method and apparatus for facilitating signal transmission. More particularly, the present invention relates to a method and apparatus for facilitating signal transmission using differential transmission lines.
2. Description of the Related Art
Signals may be transmitted in data processing systems using techniques such as signal-ended signaling and differential signaling. A signal is any data capable of transmission. Differential signaling, which uses differential transmission lines to transmit a signal, is often preferred in applications that require an extra degree of noise immunity.
A differential transmission line is a plurality of electrical conductors that complement one another in the transmission of a signal. The signal transmitted by the differential transmission line is indicated by a voltage difference between the conductors in the differential transmission line. For example, a differential transmission line may include two wires that are substantially parallel to one another, and which transmit a signal as indicated by a voltage difference between the two wires. Any noise source that induces more voltage on one conductor than the other will add a net noise in the signal that is equal to the difference in noise between the conductors.
Differential signaling may be used in different contexts. For example, differential signaling may be used in computers, circuits, computer networks, data transmission connectors, cables, power grids, low voltage applications, high voltage applications, low frequency application, and high frequency applications.
Differential signaling may be used in analog signaling, such as the analog signaling used in some audio and video systems. Differential signaling may also be used in digital signaling. For example, differential signaling is used in the EIA-422 and EIA-485 specifications for signaling. EIA-422 is the technical standard that specifies the electrical characteristics of the balanced voltage digital interface circuit. EIA-485 is an open system interconnection model physical layer electrical specification of a two-wire, half-duplex, multi-point serial connection. EIA-422 and EIA-485 are now administered by the Telecommunications Industry Association. Other exemplary uses of differential signaling in digital signaling include the use of differential signaling in the peripheral component interconnect express (PCI Express) and universal serial bus interface types.
Differential signaling may also be used in the high-speed digital serial interfaces of low voltage differential signaling, serial advanced technology attachment (Serial ATA), hypertransport, and Ethernet. Other implementations of differential signaling may be found in emitter coupled logic (ECL), positive emitter coupled logic (PECL), low voltage positive emitter coupled logic (LVPECL), musical instrument digital interface (MIDI), transition minimized differential signaling, and firewire.